1. Field of the Invention
The present inventor relates to a base station apparatus, mobile terminal apparatus and wireless access system using the apparatuses to perform a communication method which is used in a wireless internet access system where the base station and mobile terminal perform wireless communications to obtain the internet service and which is to achieve effective data transmission.
2. Description of the Related Art
Various studies have been performed to utilize over wireless mobile networks internet communication protocol TCP (Transmission Control Protocol)/IP (Internet Protocol) designed for use in cable fixed networks.
In particular, the greatest problem arising in applying TCP to wireless mobile networks is that TCP protocol detects network congestion due to TCP segment loss caused in a wireless channel of low quality, and that as a result, a TCP window is narrowed, thereby lowering throughput extremely.
In order to solve the above problem, Japanese Laid-Open Patent Publication HEI11-163947 and so on propose that a gateway apparatus on a boundary between cable communications and wireless communications divides the TCP link and performs TCP link control suitable for each link.
A conventional wireless internet access system will be described below with reference to FIGS. 1 and 2.
FIG.1 is a diagram illustrating a configuration of the conventional wireless internet access system, where “11” denotes a mobile terminal, “12” denotes abase station apparatus, “13” denotes a getaway that has control over a plurality of base station apparatuses 12, and “14” denotes a network that accommodates mobile terminal 11, base station apparatuses 12 and getaway 13.
FIG. 2 is a diagram illustrating a configuration of the gateway apparatus in the conventional wireless internet access system, where “20”, denotes the gateway apparatus, “22” denotes a cable TCP processing section (CTCP) comprised of TCP output section (TCPOS) 23 and TCP input section (TCPIS) 24, “25” denotes a wireless TCP processing section (WTCP) having wireless TCP output section (WTCPOS) 26 and wireless TCP input section (WTCPIS) 27, “21” denotes a TCP relay section for performing a data relay between cable TCP processing section 22 and wireless TCP processing section 25, “28” denotes an IP processing section comprised of IP output section (IPOS) 29, IP input section (IPIS) 31 and IP relay section (IPRS) 30 for performing a data relay between the sections 29 and 31, and “32” denotes an I/F (Interface) section.
Mobile terminal 11 connects a TCP link to a server not shown on network 14, and performs an internet access. At this point, in FIG. 1, between mobile terminal 11 and gateway 13 is connected a TCP link with parameters suitable for a wireless channel of low quality, between gateway 13 and the server is connected a conventional TCP link, and gateway 13 performs the relay between mobile terminal 11 and the server, and thereby intends to suppress the extreme deterioration on throughput.
Specific TCP relay processing will be described with reference to FIG. 2. When an arbitrary TCP segment reaches gateway apparatus 20 through I/F section 32, the segment is output to IP input section 31 to be assigned processing of either cable TCP processing 22 or wireless TCP processing section 25. In other words, when being input from network 14, the TCP segment is transferred to cable TCP input section 24, while being transferred to wireless TCP input section 27 when being input from base station apparatus 12.
Then, TCP relay section 21 performs the processing on the TCP segment so that the segment received from base station apparatus 12 is transferred to network 14, while the segment received from network 14 is transferred to base station 12 apparatus. TCP relay section 21 constructs a table with combinations of a sender and a destination IP address and of the sender and a destination TCP port, and thereby performs the relay processing on the TCP segment while uniquely identifying all the TCP links.
In the above conventional example, a plurality of TCP processing sections (cable TCP processing section 22 and wireless TCP processing section 25) has one IP processing section 28, which changes an IP address of a terminal at the time the terminal moves between subnets, using a mobile IP protocol such as Mobile IP.
However, in the above wireless internet access system, since the concept of subnets in IP is applied to wireless networks with frequent movements, inconvenience described below are apparently caused. That is, mobile terminal 11 should set an IP address belonging to a subnet that base station apparatus 12 disposes on the wireless channel, and therefore change the IP address at the same time as performing handover between subnets.
When it is considered that in the feature the widespread use of IPv6 will expand an IP address space, expected is an environment where a fixed IP address is assigned to each terminal, and a local LAN (for example, vehicle LAN) is constructed by connecting the mobile terminals over a wireless or cable link. In this case, the frequent IP address update due to the movement increases a processing load on a mobile terminal including LAN,
A high incidence of handover is predicted in a spot communication system such as a high-speed large-capacity EHF (Extremely High Frequency) access system expected to be put in widespread use in the future, whereby the above-described problem is serious in particular in such a system.